Evaluation and storage of water resources in semi-arid regions

Most Arabian countries are touched directly by the problem of deficit in hydric resources. The semi-arid and arid regions occupy the biggest surface of the national territory. The example of Algeria, the semi-arid regions occupy a surface of more then one hundred thousand square kilometres, which are characterised by pronounced deficit in rain and by a strong evaporation that is conditioned by a very positive radiation balance. The relatively humid season is constituted of episodic rains limited in the time and in the space whose mean is between 250 and 300 mm. The superficial out-flow can be observed at any moment of the year and is begotten by the violent downpours. In these regions, the lack of observation stations makes the question of the water resources estimation more delicate. Knowing the climatic factors and surface factors that are distributed harmoniously in the space, then the recourse to the methods development of territorial hydrological generalisation, which is justified for the case of the semi-arid regions and it permits to satisfy the need of resource assessment. Also, the verification of the genetic dependence between the mean out-flow through the years and the factors that determine it, makes the goal of this work. The hydrological cartography can be a practical tool in hydraulic improvement in semi-arid region. The proposed harnessing consist in storing the waters of the superficial out-flow in restraints, to the suitable place, permitting the refill of phreatic sheet — the unique soft water resource for the man and the animals — that can be captured by the drilling of wells. This communication has for object to show the possibility of cartography of the mean out-flow through the years and to propose a workmanship of retention and infiltration for the refill of phreatic sheet.